Schlumberger

Technical Paper: Field Test Results Of A New-Genaration Large-Bore Rotary Coring Tool

Society: SPWLA
Paper Number: SPWLA 52nd Annual Logging Symposium
Presentation Date: 2011
 

Abstract

Wireline sidewall cores have a well-established role in the formation evaluation program in providing key rock properties. While they provide a subset of the exhaustive information obtainable from continuous core, for reasons of operational efficiency they are often deemed to be the most practical option.

Although the ability to perform routine core analysis (RCAL) measurements on sidewall core samples improved significantly with the introduction of the first rotary sidewall coring tools in the 1980s, significant limitations remain related to the relatively small size of the sample. Among other challenges, measurement uncertainty is higher compared with core plugs, and in heterogeneous formations the smaller volume of rock is expected to be intrinsically less representative of bulk reservoir properties. Many special core analysis (SCAL) and rock mechanics methods are not considered to give valid results or cannot be performed owing to insufficient volume of core material.

To address the given challenges and improve the range of tests that can be accurately performed on sidewall cores, we introduce a new wireline rotary sidewall coring tool that acquires samples slightly larger than standard laboratory core plugs, 1.5 in in diameter by 3 in in length. Every aspect of the new coring system has been engineered to enable easy and reliable wellsite operation with real-time intelligent drilling control and efficient recovery in a broad range of lithologies. An innovative system of core handling and core preservation techniques ensures the recovery, traceability, and integrity of each core from the moment it is cut downhole until delivery to the laboratory.

We review the results of six months of field testing in both soft and hard formation types (shale, sandstone, and carbonate) with respect to core recovery, core quality, and the resulting possibilities for core analysis. We provide a laboratory perspective on the expected efficacy of common measurements carried out on the new sidewall cores compared with those from standard rotary sidewall cores, and find that for most analyses we should expect low uncertainty similar to core plugs cut from whole core.

A case study from North America is presented, illustrating an optimized process for unconventional reservoir analysis that begins with careful selection of sidewall coring points based on log interpretation and the operator’s analysis requirements. During core acquisition, the usefulness of novel tool features for downhole core assurance is demonstrated, and it is shown that the full range of analyses required may be carried out on the new large, high-quality sidewall core, where previously several sidewall cores would have been required. The end result is that an extended reservoir interval could be successfully characterized from a single sidewall coring descent, where previously at least three sidewall coring descents or multiple stands of whole core would have been required.

Request More Information